Two-piece solid golf ball

Abstract

In a 2-piece solid golf ball comprising a solid core and a cover, the golf ball has a weight of 41-44.5 grams, the cover is formed of a thermoplastic resin having a Shore D hardness of 50-68 degrees, and the solid core has a surface hardness of 65-85 degrees and a center hardness of 60-80 degrees as measured by a JIS-C scale hardness meter, with the surface hardness>/= the center hardness+5. Despite a light weight, the golf ball is improved in flying distance and feel when hit at a relatively low head speed of 35-40 m/sec. The golf ball is thus appropriate for players of the beginner to middle rank.

We claim: 
     
       1. A two-piece solid golf ball comprising, a solid core and a cover enclosing the core and having a multiplicity of dimples formed on its surface, wherein the golf ball has a weight of 41 to 44.5 grams,   the cover is formed of a thermoplastic resin having a Shore D hardness of 50 to 68 degrees, and   the solid core has a surface hardness of up to 85 degrees and a center hardness of up to 80 degrees as measured by a JIS-C scale hardness meter, the surface hardness being greater than the center hardness by at least 5 degrees.   
     
     
       2. The two-piece solid golf ball of claim 1 wherein the number of dimples formed on the cover surface range from 360 to 450 and each have a diameter of 2.0 to 4.2 mm, a depth of 0.15 to 0.30 mm, and a V 0  value of at least 0.4 wherein V 0  is the volume of the dimple space below a plane circumscribed by the dimple edge divided by the volume of a cylinder whose bottom is the plane and whose height is the maximum depth of the dimple from the bottom. 
     
     
       3. The golf ball of claim 2 wherein 0.65≧V 0  >0.42. 
     
     
       4. The two-piece solid golf ball of claim 1 wherein the dimples include dimples of one type having a larger diameter and dimples of another type having a smaller diameter, the dimples of the one type having a greater depth than the dimples of the other type. 
     
     
       5. The golf ball of claim 1 wherein 20≧H s  -H c  ≧5 where H s  is the surface hardness of the core and   H c  is the center hardness of the core.   
     
     
       6. The golf ball of claim 1 wherein said cover has a thickness in the range of 0.85-2.85 mm. 
     
     
       7. The golf ball of claim 1 wherein the surface hardness of said core is greater than said center hardness of said core by at least 7 degrees. 
     
     
       8. The golf ball of claim 1 wherein said center hardness of the core is at least 60 degrees. 
     
     
       9. The golf ball of claim 1 wherein said surface hardness of the core is at least 65 degrees. 
     
     
       10. The golf ball of claim 1 wherein said solid core has a diameter in the range of 37 to 41 mm. 
     
     
       11. The golf ball of claim 1 wherein said solid core has a weight in the range of 27 to 40 grams.